1. Field of the Invention
This invention relates to a wafer rotary holding apparatus that can hold a wafer with no contact to a rear surface of the wafer, using a reduced pressure created by a fluid on an upper surface of a rotary disk, discharged outwardly by centrifugal force due to rotation of the rotary disk, and to a wafer surface treatment apparatus with a waste liquid recovery mechanism that, when a surface of the wafer is treated with a treatment liquid or a cleaning liquid, waste liquids can be separately recovered in an efficient manner according to kinds of the treatment liquid and the cleaning liquid.
2. Description of the Prior Art
In a semiconductor fabrication process, steps of performing various kinds of treatment on a wafer during rotation, such as spin etching, spin drying and spin coating, have increased in recent years. To definitely name apparatuses for such steps, there have been known a spin-etching apparatus, a spin-drying apparatus, a spin-coating apparatus and so on. In such apparatuses of the prior art, the following ways for fixing a wafer have been adopted: a wafer is suction-fixed on a suction-chuck base using a vacuum source, or a wafer is fixed on a suction-chuck base using a vacuum force created there by a compressed air or gas from a supply source.
The prior art apparatuses, however, have required a vacuum source apparatus, a compressed air supply apparatus, a compressed gas supply apparatus and so on, which are additionally provided thereto, thereby resulting in cost increase due to installment thereof. In addition to the cost increase, there has arisen another problem because of hardship in adjustment of degrees of reduction or increase of pressure, which leads to a phenomenon that a wafer is deformed, for example, sagged under an influence of a pressure in the case where the wafer as thin as to be easy to be affected by the pressure, for example of a thickness of 0.1 mm or less, is fixed.
Further, a wafer as thin as of the order of 100 xcexcm or less naturally has bow in many cases, and therefore, suction-chuck of the wafer has not been successfully effected because of the bow in the prior art apparatuses described above. For this reason, in the case of a wafer with bow, there has occurred a need for time and labor with which a wafer is corrected on the bow, for a procedure has actually been adopted where the wafer is corrected on the bow and thereafter, the wafer is suction chucked.
As treatment for a surface of a wafer in a device fabrication process, there can be named: etching treatment for removing a damage layer after back side grinding, coating of a photo resist on the wafer, developing of the wafer on which circuit patterns are exposed, a photo resist is coated and semiconductor circuits are printed, cleaning of a surface of the wafer and so on.
An apparatus for use in the wafer surface treatment includes: a wafer rotary holding apparatus which chucks and rotates a wafer; a treatment liquid supply means supplying a necessary treatment liquid (a chemical liquid) onto the upper surface of the chucked wafer; a cleaning liquid supply means supplying a cleaning liquid onto the upper surface of the wafer; and other means (for example, Japanese patent Laid-open Publication No. 8-88168).
Etching for removing a damage layer after a prior art back side grinding, for example, has sufficiently been concluded with one time of usage of a mixed acid (for example, hydrofluoric acid, nitric acid and so on) and in this case, it is only required after the etching to recover the used treatment liquid (for example, the used mixed acid) and the used cleaning liquid as disclose in the above publication.
At present, however, a necessity has already showed up of surface quality improvement after the above described etching and it has been common to effect one or more times of additional etching for surface quality improvement following the first etching described above. With plural times of surface treatment in this way, a new problem has occurred since a process time becomes totally longer due to the surface treatment, thereby leading to reduction in productivity. Further, since a plurality of treatment liquids (chemical liquids) are in use, a necessity has arisen of an apparatus by which three (3) or more kinds of waste liquids can be recovered, wherein requirement is beyond a capacity of a prior art apparatus by which only two (2) kinds of waste liquids including one kind of a treatment liquid and a cleaning liquid are recovered.
Further, on the other hand, while there has be required single side treatment in recent years in the case where a very thin wafer of 100 xcexcm or less in thickness is etched or cleaned, a rotary holding means of a novel type has been desired in order to cope with such a requirement since it is difficult to hold a wafer while rotating with prior art means that holds a wafer while rotating by suction-chucking the lower surface thereof.
The present invention was made in light of the above described problems of the prior art. Accordingly, the invention has two objects: one is to provide a wafer rotary holding apparatus by which a reduced pressure is created on an upper surface of a rotary disk by a simple and easy-to-make mechanism with no need of any of a vacuum source apparatus, a compressed air supply apparatus, a compressed gas supply apparatus and other apparatuses in use; a wafer can be held while rotating with no contact to a rear surface thereof; a degree of pressure reduction can be adjusted with ease and even a thin wafer (of 0.1 mm or less in thickness) can be held while rotating with no deformation; the wafer with bow can be held while rotating with no correction of the bow; furthermore a very thin wafer of 100 xcexcm or less in thickness can be held while rotating using only contacts with the periphery of the wafer; and in addition, cleaning using a ultra-sonic jet nozzle and brush cleaning can also be employed, and the other is to provide a wafer surface treatment apparatus having a waste liquid recovery mechanism by which wastes liquids, especially three or more kinds of waste liquids, can be separately recovered in a continuous, efficient manner according to kinds of a treatment liquid and a cleaning liquid and therefore productivity can be increased.
In order to solve the above described problems, the invention is directed to the following apparatuses.
A wafer rotary holding apparatus of the invention includes: a rotary disk on which a fluid flow path is formed; a through hole formed in a central section of the rotary disk; and a plurality of wafer rests provided on an upper surface of the rotary disk, wherein a wafer is placed on the wafer rests, above the rotary disk with a gap therebetween, and wherein when the rotary disk is rotated, a fluid in the fluid flow path is discharged outwardly by centrifugal force due to rotation; thereby a reduced pressure is created in the fluid flow path and kept as far as the rotary disk is rotated, through a process in which a fluid is drawn by sucking force of the reduced pressure from the lower surface side of the rotary disk through the through hole, and the fluid drawn is supplied onto the upper surface of the rotary disk to be outwardly discharged in a continuous manner passing through the fluid flow path, with the result that the wafer is drawn downwardly by the sucking force of the reduced pressure and fast held on the wafer rests while rotating.
It should be appreciated that there arises an advantage in that even in the case where bow is inherently present in a thin wafer of the order of 100 xcexcm or less in thickness, when placing and holding the wafer on the wafer rotary holding apparatus as it is, the wafer can be held while rotating with no troubles because the bow is cancelled by centrifugal force due to the rotation.
A wafer rotary holding apparatus of the invention preferably further includes: fluid forcible supply means supplying a fluid forcibly through the through hole from the lower surface side of the rotary disk, wherein the fluid is supplied through the through hole in a forced manner from the lower surface side of the rotary disk while keeping the reduced pressure. With such a construction, there arises an advantage in that a chemical liquid supplied onto the upper surface of the wafer to treat the upper surface thereof can be prevented from creeping over onto the lower surface of the wafer.
A construction is preferable in which straight or curved blades are provided in a radial state, or a single curved blade is provided in a spiral or volute state on the upper surface of the rotary disk and the fluid flow paths or path is formed in spaces between the upper surface of the rotary disk and a lower surface of the wafer, being partitioned by pairs of opposed blades or blade portions.
A construction is also possible in which a rotary shaft through which a hollow section in communication with the through hole is formed along the axial direction thereof is vertically provided on the central section of the lower surface of the rotary disk and when the rotary shaft and the rotary disk are rotated, a fluid taken in by suction from a lower end opening of the hollow section of the rotary shaft is supplied onto the upper surface of the rotary disk passing through the hollow section and the through hole.
If a construction is adopted in which a wafer rotary holding apparatus of the invention further includes pressure reduction control means controlling a reduced pressure in the fluid flow paths by adjusting a degree of opening of the hollow section, mounted at a proper position along the rotary shaft, a trouble such as that the wafer would otherwise be deformed by excessively strong sucking force is completely eliminated since a degree of the reduced pressure can be freely set according to a thickness of the wafer.
The wafer rests can be constructed with lower side guide pins receiving the lower surface of a wafer and outer side guide pins receiving the outer side surface of the wafer. Further, while the wafer rests may be disposed at any positions on the upper surface of a rotary disk as far as a receiving action is not hindered, the wafer rests can advantageously be placed on the upper surfaces of the blades since spaces above the upper surface of the rotary disk can be effectively exploited.
A construction is conceived in which a baffle plate is provided above the through hole formed in the central section of the rotary disk and a fluid supplied onto the upper surface of the rotary disk passing through the through hole is guided in a blade direction by the baffle plate. With such a construction applied, advantages are enjoyed since the fluid does not blow directly to the lower surface of a wafer and therefore, an accident in which the wafer is contaminated with impurities and so on can be prevented from occurring even when impurities or the like are mixed into the fluid, or upward blow-off of the fluid can be prevented from occurring when the wafer is accidentally broken during operation.
If an orientation flat receiver receiving an orientation flat of the wafer or a notch receiver receiving a notch of the wafer is provided on the upper surface of the rotary disk, a wafer is engaged with the upper surface of the rotary disk and therefore, both rotates as one body all time. Consequently, an advantage is enjoyed since even when a chemical liquid or the like liquid is poured onto the upper surface of a wafer held while rotating and a force acts on the wafer in a direction opposite from a direction of rotation, then the wafer continues to rotate in one body with the rotary disk all time with no discrepancy in speed of rotation therebetween, thereby causing no problem due to relative displacement of rotation therebetween, which will be described later.
As the fluid, there can be used: a gas and/or a liquid; that is a gas in a single state, for example air, a liquid in a single state, for example pure water or a chemical liquid, or a mixture thereof.
A wafer surface treatment apparatus with a waste liquid recovery mechanism of the present invention is a wafer surface treatment apparatus treating a surface of a wafer with each of a treatment liquid and a cleaning liquid, including: a wafer rotary holding apparatus holding a to-be-treated wafer while rotating; and a waste liquid recovery mechanism provided around the periphery of the wafer rotary holding apparatus in a vertically movable manner, wherein the waste liquid recovery mechanism is constructed of a plurality of annular waste liquid recovery troughs which are also vertically movable relative to each other or one another and the annular waste liquid recovery troughs are selectively used according to kinds of the treatment liquid and the cleaning liquid, such that the respective waste liquids are separately recovered. By moving upward or downward the above described annular waste liquid recovery troughs in a continuous manner, the treatment liquid and the cleaning liquid which have been used in respective wafer surface treatments can be recovered in a continuous manner, thereby enabling a production efficiency to increase.
With three annular waste liquid recovery troughs in use, there can be enjoyed an advantage in making it possible to recover three kinds of waste liquids.